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Vision-enabled barcode readers with the ease-of-use and cost of laser scanners

The concept of “traceability” is now firmly established in the automotive supply industry. Hundreds of thousands of transport trays play a key role in the internal transport system of the Continental plant in Frankfurt, Germany. Continental, an international automotive supplier, moves the majority of its components on these transport trays. The standardized trays sometimes cover enormously long distances in their productive life and form an important basis of internal logistics.

Complexity requires control

Such a highly distributed production and supply network requires precise control and reliable inspection. Barcodes or 2-D matrix codes give the trays their unique identity. To guarantee secured logistics, it is required that the location of a batch of individual parts should be traceable at all times. To achieve this, it is necessary to provide inspection units at regular intervals and at critical interfaces. This is still often implemented today in the form of employees laboriously reading the codes with handheld scanners, which update the location of the transport tray, and this is how the parts required in the production process are updated in the logistics system.

Location, type and content

Continental in Frankfurt has now gone an important step further. In collaboration with the image processing specialist Stemmer Imaging, the formerly manual entry of individual tray barcodes has been automated using In-Sight® 5605 high-resolution intelligent vision systems from Cognex. Thanks to the highest resolution of 5 megapixels, the vision system recognizes and reads the codes on tall stacks with different numbers of trays within a few milliseconds.

“The vision system first identifies the location of up to eleven codes in the stack, then differentiates their type, i.e., whether they are barcodes or 2-D matrix codes, and then reads the information into the logistics system,” explained Marc Wilhelm of Continental, describing the process on the station that he implemented as the project manager together with his development team. “The bottommost code in the tray stack serves as the master code by means of which the entire stack can be identified. At a downstream inspection point, it is then not necessary to read all of the individual codes again; checking the bottommost code is sufficient.”

No “stowaways”

In addition to the code recording, a measurement of the stack height is also performed. This serves as an additional verification of the reading result. “If, for example, the vision system detected only a single code, there would be a risk that other unencoded trays could go past as stowaways,” said Wilhelm. According to him, the height measurement reliably rules out this unlikely but conceivable security vulnerability.

Compared to the former manual scanning, the new system has many advantages. The process is significantly faster and eliminates the potential for errors in manual work. Duplicate or unscanned codes are therefore a thing of the past at Continental.

Helpful partner

Wilhelm emphasized the good co-operation with Stemmer Imaging, which offered a great deal of help in planning and implementing the system: “During the design phase, we were able to use the Stemmer Imaging laboratory to conduct preliminary tests on the possible image processing components and could already select them to a large extent. The final specification was then determined by us on site using loaned equipment.”

The co-operation in advance, however, went even further, according to Wilhelm: “Stemmer Imaging gave us strong support in developing the software and also conducted a training course near the end of the project, which deepened our knowledge of image processing even further. Obtaining all of the necessary components from a single source and being able to use our partner’s comprehensive range of services was in my opinion very helpful to the project.”

Meeting the challenge

In addition to the different colors of the various trays, the fact that the leading and trailing edge zones of the barcodes were often too small presented a key challenge that had to be overcome by the image processing experts at Stemmer Imaging,. These edge zones are precisely what were needed to identify the code before reading it.

To solve this task, Stemmer Imaging made use of Cognex’s PatMax® technology. “PatMax uses a sophisticated technology for geometric pattern matching to be able to locate parts reliably and precisely even in the toughest of conditions,” explained Christian Berg of image processing solutions sales, who led the project on behalf of Stemmer Imaging. “PatMax captures the geometry of the code with the help of several boundary curves that are not tied to any pixel grid, and then looks for similar shapes in the image, without making use of specific greyscale values. The result is a significant improvement in the localization ability and precision, even with varying angles, sizes and shading.”

Stemmer Imaging thus succeeded in clearly reading formerly unreadable codes. With the equally innovative and proven Cognex technology In-Sight 5605 plus PatMax and the support of the Puchheim image processing experts, the pilot project at Continental in Frankfurt is a pioneer of a secure and fast-moving logistics chain which, according to Wilhelm, may soon also be implemented similarly in other logistics applications at the Frankfurt location.